This invention relates to 2-aryltetraazaindenes of the general formula I ##STR2## wherein --A-- is --N.dbd.CH--CH.dbd.N-- or --CH.dbd.N--N.dbd.CH--, Ar is unsubstituted phenyl or phenyl mono-, di- or tri-substituted by hydroxyl, mercapto, dialkylamino, trifluoromethyl and/or --Z-- R groups, Z is --O--, --S-- or --SO-- and R is alkyl, alkenyl, alkynyl or cyanomethyl, the alkyl, alkenyl and alkynyl groups each having up to 5 C atoms, or a physiologically acceptable salt thereof.
These compounds encompass 1,3,4,7-tetraazaindenes (imidazo(4,5-b)pyrazines; cf. "The Ring Index", 2nd Edition, American Chemical Society, 1960, No. 1176; formula Ia) and 1,3,5,6-tetraazaindenes (imidazo(4,5-d)pyridazines; cf. "The Ring Index", l.c., No. 1177; formula Ib): ##STR3## German Offenlegungsschrift No. 2,305,339 discloses similar compounds.